Telephone system



Nov. 27, 1945. R. H. HERRICK 2,339,556

TELEPHONE SYSTEM Filed March 17, 1944 2 Sheets-Sheet 1 TONE B USY TONE MULTIPLE T0 1| CONNECTOR BANKS u. MULTIPLE TO OTHER FINDERS IIO CIRCUIT 1 common STARTING m INVENTOR.

aoswsu. H. HERRICK ATTORNEY R. H. HERRICK TELEPHONE SYSTEM Nov. 27, 1945.

Filed March 17, 1944 2 Sheets-Sheet 2 MULTIPLE T0 FINDER BANKS mosmzzoo 59:". 3

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. mmvron. ROSWELL H. HERRIOK ATTORNEY Patented Nov. 27, 1945 TELEPHONE SYSTEM Roswell H. Herrick, Oak Park, 111., assignor to Automatic Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application March 17, 1944, Serial No. 526,871

1'7 Claims.

The present invention relates to telephone systems in general, but is concerned more particularly with automatic telephone ystems used to give service to subscribers in rural districts.

The principal object of the present invention is the production of new and improved circuit arrangements to provide automatic telephone service in rural areas, where the lines may have such a high resistance and be in such a relatively poor state of repair as to preclude the use of conventional automatic telephone switching equipment, without the necessity of rebuilding the outside plant. One possible solution to this problem is disclosed in Patent No. 1,914,357, granted June 20, 1933, to Charles R. Brooks. This proposed solution require the use of a special repeater with each line in conjunction with conventional switching circuits. The present invention eliminates the need for individual repeaters by incorporating new and improved control circuits in the switching equipment proper. These improvements consist of novel circuit arrangements incorporating vacuum tubes whose input circuits are controlled by current from the local battery at the substation and whose output circuits are used for controlling the starting of the finder switches when a call is initiated, stopping the finder when it reaches the calling line, stepping the connector switch to the called line, completing the connection when the called party answers, and releasing the connection when both parties disconnect.

One of the features of the invention isth-e provision of a vacuum tube circuit common to all of the lines in the exchange that will respond to the initiation of a call from any substation and start a finder switch searching for the calling line. This feature reduces the amount of individual line equipment required to a single relay thus making the system economical.

According to a modification of the invention the need for a separate vacuum tube circuit to detect the initiation of a call is eliminated by extending a circuit common to all of the lines through a distributor switch to a vacuum tube in the finder switch, and providing means to enable this vacuum tube to start the finder when a call is initiated in addition to its other functions.

A further feature of the present invention is the elimination of the magneto from the substation equipment, the supervisory and diallin operations being controlled through the use of the local battery at the substation.

Other objects and features of the invention will appear upon a further perusal of the specification in connection with the accompanying drawings comprising Figs. 1 and 2, which show, by means of the usual circuit drawings, a sufllcient amount of equipment in a telephone system embodying the features of the invention to enable the invention to be understood.

Fig. 1 shows two of the substations, A-t and B-l, connected to the exchange equipment through lines I31 and I 38, together with the common starting circuit, distributor switch, and one of a plurality of finder-connector links.

Fig. 2 is a modification of Fig. 1 in which the common starting circuit of Fig. 1 is eliminated.

The various stepping switches shown are the type in which every movement of the switch is controlled by the stepping magnet, the actual movement of'the wipers occurring during the release of the magnet.

The vacuum tubes shown in the drawings are the pentode type. Of course any other type may b used but the pentode is preferable since it can be designed to have a sharp cut-off characteristic thus requiring only a very small change in grid voltage to control the relay in its plate circuit.

While a plurality of batteries are shown in the drawings it i to be understood that there is preferably but one battery for the relays, switches, and filaments of the vacuum tubes having its positive pole connected to ground, and but one battery for the plate and screen-grid circuits of the vacuum tubes having its negative pole connected to ground.

The equipment shown is sufficient for a ten line exchange. The number of finder-connector links required depends on the number of simultaneous conversations the exchange must handle. The distributor switch is shown wired for three finder-connector links.

Referring in greater detail to the equipment shown in Fig. 1, the substation rA-l is the usual local battery type modified by the addition of a calling device, a resistor, and a condenser. Provision is made for allowing a weak direct current to flow over the'line conductors to the exchange equipment, when the substation i in use, for control purposes. The calling device interrupts this direct current circuit to control the stepping switches.

Each subscribers line terminates on the springs of a line relay at the exchange. The lines are all normally connected to the input circuit of a common vacuum tube through back contacts of the line relays. v

The removal of the receiver from the hookswitch at any of the substations will cause a current to flow over the line conductors through the back contacts of the line relay and through resistor I39. The resultant voltage drop across resistor I39 reduces the grid voltage on vacuum tube I40, which is normally biased to cut-off by the voltage drop produced in resistor MI by the filament current. The plate current of vacuum tube I40 then increases and operates relay I I0, which will in turn cause the finder switch previously selected by the distributor switch to start searching for the calling line. The finder switch will test each line in succession by disconnecting it from the input circuit of the common vacuum tube I40 and transferring it to the input circuit of vacuum tube I42 in the finder. Vacuum tube I42 is also normally biased to cut-off by the voltage drop produced across resistor I43 in its filament circuit. When the finder reaches the calling line the grid voltage on vacuum tube I42 will be reduced due to the voltage drop produced across resistor I44 by the current flowing over the line from the local battery at the calling substation. The plate current of vacuum'tube I 42 therefore increases and operates relay I05 which causes the release of the common starting equipment and prepares the circuits to the connector which is associated with it.

When the subscriber operates the callin device at the substation the direct current flowing over the line and through resistors I44 and I45 is periodically interrupted. The resulting changes in the grid voltage of vacuum tube I42 cause corresponding interruptions in its plate current. Relay I05 follows the interruptions in plate current and repeats the impulses to the stepping magnet of the connector switch causing it to advance the wipers to the bank contacts correspondin to the called line. At the completion of dialling the connector will test to determine whether the called line is idle or in use. If it is in use the connector will'connect busy tone to the calling line. If the called line is free it will connect a low frequency alternator G-I to the called line to operate the ringer at the called substation. Vacuum tube I 46 is normally biased to cut-ofi by the voltage drop produced across resistor I41 by its filament current. When the called subscriber answers by removing his receiver from the hookswitch the grid voltage of vacuum tube I46 will be reduced by the voltage drop across resistor I43 caused by the current flowing over the line from the local battery at the called substation. The ,plate current of vacuum tube I46 consequently increases and operates relay I01 which prevents further application of ringing voltage to the line and establishes a transmission circuit between the calling and called lines. The input circuits of vacuum tube I 42 and I46 are now connected in multiple so that as long as either party remains connected the grid voltage on vacuum tubes I42 and I46 will be reduced and will maintain the connection. When the last party restores his receiver to the hookswitch vacuum tube I42 will be biased to cut-off causing relay I05 to release. All relays in the finder-connector link will release and cause the connector switch to restore to its normal position but the finder switch will remain in the position it occupied durin the call.

Referring to Fig. 2, the substation and line equipment is identical to that previously described. In this case the lines are all normally connected to the input circuit of vacuum tube 242 through the distributor switch and the 11th bank contacts of the finder switch.

The removal of the receiver from the hookswitch at any of the substations will cause a current to flow over the line conductors, through the back contacts of the line relays, wipers 2I1 and 2I8 of the distributer switch DS-2, wipers 2I2 and 2I3 of the finder switch, and through resistors 244 and 245. The resultant voltage drop across resistor 244 reduces the grid voltage on vacuum tube 242. The plate current of vacuum tube 242 therefore increases and operates relay 205 which starts the finder switch in motion. As the finder switch steps from the 11th position the input circuit of vacuum tube 242 is disconnected from the distributor switch causing the grid voltage of vacuum tube 242 to return to cut-off and release relay 205. This causes the finder switch to continue stepping until the grid voltage of vacuum tube 242 is again reduced when the calling line is encountered. The remaining functions are the same as previously described for Fig. 1 except that the finder switch is returned to the 11th position at the conclusion of the call to prepare the path to the input circuit of a vacuum tube 242 from the distributor switch in preparation for answering a succeeding call.

Having briefly described the functions of the apparatus I will now proceed to describe in detail the operations involved when a subscriber at substation A--I of Fig. 1 calls another subscriber at substation BI.

When the subscriber at substation A-I removes the receiver I21 from the hookswitch I26 a circuit is established through the transmitter I28, the primary winding of the induction coil I29, the local battery I3I, and the contacts of the hookswitch I26. The local battery I3I is also connected across the line I31 in series with resistor I32 and the interrupter springs I34 of the calling device I36. A third circuit is established between one side of line I31, the oil-normal springs I35 of the calling device, condenser I33, the secondary winding of the induction coil I29, the receiver I21, and through make springs of the hookswitch I26 to the other side of line I31. The ringer I30 is also disconnected from the line to prevent it from shunting any of the voice currents from the receiver. The connection of the local battery across the line through resistor I32 allows a weak current to flow through the line conductors I31, the back contacts of the line relay, and through resistors I39 and I49 at the exchange. Resistor I49 prevents an accidental short-circuit on line I31 from making the common starting circuit inoperative. The battery I3I at the substation must be poled so that this flow of current through resistor I39 will decrease the negative grid bias on vacuum tube I40. The normal grid bias for this tube is obtained from the voltage drop across resistor I 4|, and is sufllcient to reduce the plate current to the cut-off point. When the net grid bias on vacuum tube I40 is reduced, by the application of battery to to the line at any one of the substations, its plate current will increase and cause the operation of relay IIO.

Relay IIO operates, connects ground thru wiper I2I of the distributor switch DSI to wiper III of finder switch FSI, and closes a circuit through wiper I20 of DSI to rela I03 and the stepping magnet FSM--I of the finder switch FS-I Relay I03 operates, closes the circuit to the filaments of vacuum tubes I42 and I46, and prepares a multiple circuit to the stepping magnet 5 FSM-I from wiper II4 of FSI.

The stepping magnet of FSI operates and opens its own circuit at its interrupter springs I49, causing it to restore and advance the wipers one step. This operation is repeated as long as the circuit to the stepping magnet is completed through its interrupter springs. As the wipers are advanced over the bank contacts, the ground on wiper III of FSI operates the line relays IOI, I02, etc., in succession. The operation of each line relay transfers its associated line from the common starter tube I40 to vacuum tube I42 through wipers H2 and H3 of the finder switch FS--I. If only one subscriber is attempting to make a call the operation of the line relay associated with that subscribers line will allow the grid bias of vacuum tube I40 to return to its normal value thus causing the release of relay H and stopping the motion of the finder switch FS--I by opening the circuit to the stepping magnet FSM-I. However, it is possible that several subscribers might be attempting to make calls at the same time. In this event relay IIO will remain operated when one of the lines initiating a call is disconnected from the input circuit of vacuum tube I40 by the finder switch, but a direct current will flow through resistors I44 and I45 from that line and will decrease the grid bias on vacuum tube I42 causing relay I'05 to operate and open the circuit to the stepping magnet of the finder switch to prevent it from advancing farther. Of course, any line which has already established connection with a finder would also have a direct voltage on it that would cause relay I in the second finder to operate. In order to make the finder switch that is searching for a calling line pass over lines that have already been answered rovision is made to connect ground to wiper II4 of the finder switch after it has found a line. When a second finder that is searching for a calling line reaches a line that has already been answered the ground on wiper I I4 from the first finder will maintain the circuit to the stepping magnet FSM-I and relay I03 of the second finder, thus forcing the second finder switch to advance despite the operation of relay I05.

When the calling line is found the operation of relay I05 opens the circuit to relay I03 and the stepping magnet of FS-I, if it has not already been opened by the release of relay H0 as previously described.

Relay I03 restores and closes the circuit to relay I04.

Relay I04 operates, closes a multiple circuit to the line relay IOI of the callin line thru wiper III of the finder switch; FS--I, closes a multiple circuit to the filaments of vacuum tubes I42 and I46, closes the circuit to relay I06 from the 11th bank contact of wiper I25 of the connector switch (IS-I, grounds wiper I I4 of the finder switch to prevent other finders from stopping on the same line, closes the circuit to the stepping magnet DSM-I of the distributor switch DS-I through its interrupter springs I50 and wiper H0 of DS--I and removes a multiple ground from bank contact II of wiper [I9 of DS-I.

The stepping magnet of the distributor switch DS-I now advances its wipers one step to route the next call to the following finder. If the next finder is in use the circuit to the stepping magnet of the distributor switch will be maintained.

from ground on wiper II9 of DSI and will cause the distributor switch to continue stepping until an idle finder is found. If all of the finders are in use there will not be any ground on bank contact II of wiper II9 of DS-L- The distributor switch will therefore stop when it reaches the 11th step and will wait until a finder becomes idle before continuing its search. This avoids unnecessary wear of the distributor switch.

' Relay I IIB operates over the circuit closed by the operation of relay I04, prepares the circuit to relay I08 from wiper I22 of CSI, and prepares its own holding circuit.

' The operation of relay I04 also connected dial tone to the calling line to inform the subscriber that the equipment was prepared for impulsing by the calling device.

When the subscriber dials the number of the desired line by means of the calling device, the direct current flowing through the line and resistors I44 and I is interrupted by the calling device causing a corresponding number of interruptions to occur in the plate current of vacuum tube I42. The off-normal springs I35 on the calling device I36 opens the circuit to the receiver I21 during impulsing to prevent the subscriber from hearing any objectionable clicks due to the transient currents created by the interruption of the direct current path by the interrupter springs I34 of the calling device I36.

Relay I05 follows the interruptions in plate current of vacuum tube I42 and restores a number of times corresponding to the digit dialled. Each time relay I05 restores it opens the circuit to relay I04, closes a holding circuit to relay I06, and closes the circuit to the stepping magnet CSM-l of the connector switch CS-I.

Relays'IM and I00 are slow to release and therefore remain operated during dialling. The operatingcircuit to relay I06 is opened when the connector switch CS-I leaves its normal position but remains operated during dialling from the impulses it receives from a back contact of relay I05.

Each time the circuit to the stepping magnet (ISM-4 of the connector switch CSI is closed by the restoration of relay I05, stepping magnet CSM--I operates, and each time the circuit is opened it releases and advances the wipers of 45 CS-I one step. On the first step the circuit to relay I09 is closed from wiper I25. Relay I09 operates, removes dial tone from the calling line and prepares the ringback tone circuit.

As the wipers of the connector switch advance over the bank contacts the circuit to relay I08 will be closed from ground on wiper I22 when a busy line is passed over. Rela I08 will operate if this occurs but will not lock since relay I06 remains operated during dialling and keeps its locking circuit open. At the end of the last impulse relay I05 will be operated, the wipers of CS-I will rest on the bank contacts of the called line and the holding circuit to relay I06 will be open at a back contact of relay I05. In case the called line is busy relay I08 will be operated when relay I06 restores and will lock to ground from wiper I25 of CS--I through break springs of relay I06. The operation of relay I08 prevents grounding wiper I22 of CS-I so as not to interfere with the connection previously established with the called line by another switch, opens the circuits to wipers I 23 and I24 of CSI to prevent the application of ringing current to the called line, and connects busy tone to the calling line to inform the calling subscriber that the called line is in use.

If the called line is not in use relay I08 will not be operated when relay I06 restores. In this case the restoration of relay I06 closes a circuit to the line relay I02 of the called line through wiper I22 of CS-I, causing the line relay to operate and connect the line I38 to the banks of CS-I, connects the ringing generator G-I' through springs I5I and I52 of the interrupter relay I to the called line to operate the ringer at the substation, and opens the circuit to the stepping magnet of CS-I at a second point to prevent further dialling.

' The ringing generator is connected to the called line when relay I00 is operated. The rin ing voltage is also applied to the calling line thru make springs on relay I04, break springs on relay I 08, make springs on relay I09, and through condensers I56 and I! which have a high reactance at the ringing frequency and permit only a weak current to flow in the calling line which serves to inform the calling subscriber that the called subscriber is being signalled. In addition to springs I5I and I52 for interrupting the circuit to the ringing generator, relay I00 is also equipped with a pair of springs I53, I54, etc., for each finder-connector link. These additional springs are closed at the same time that the circuit to the ringing generator is closed by springs I 5! and I52. Springs I53 are used to short-circuit resistor I48 and thus prevent the ringing voltage from affecting vacuum tube I46. Springs I54, I 55, etc., serve a similar purpose in other connectors. During the periods when the circuit to the ringing generator is open, vacuum tube I46 tests the called line for answer supervision. Dur ing the first silent interval after the called party answers the grid bias of vacuum tube I45 will be reduced by reason of the direct current flowing through resistor I48 from the local battery at the called substation. This will permit the plate current of vacuum tube I46 to increase and operate relay I01.

Relay I01 operates, closes its locking circuit through resistor I59, opens the circuit from the interrupter relay springs I53 to resistor I48, and transfers the called line from the ringing generator G-I to the calling line, thereby establishing the talking circuit. Resistor I32 and condenser I33 in the subset form a simple filter circuit that isolates the voice frequency and the direct current circuits. Since the calling and called lines are now directly connected the grid bias for vacuum tube I42 will be reduced due to the current flowing through resistor I44 from the local batteries at the calling and at the called substations as long as either party keeps his receiver oil of the hookswitch. When both parties restore their receivers the grid bias on vacuum tube I42 will increase to the cut-off point causing its plate current to fall and release relay I05. Relay I05 restores and opens the circuit to relay I 04. Relay I04 restores, opens the circuit to the line relay I02 of the called line through wiper I22 of CSI, opens the circuit to the line relay ml of the calling line through wiper III of FS-I, opens the ringing generator and tone circuits to prevent interference with other lines, opens the filament circuits of vacuum tubes I42 and I46, opens the locking circuit to relay I01, removes the ground from wiper II4 of FS-I, removes the ground from the 1st bank contact of wiper II!) of DSI, grounds the 11th bank contact of wiper II9 of DS-I, and closes the circuit to the stepping magnet CSMI of the connector switch CS-I through its interrupter springs I58 and wiper I25 of CSI.

Relay I01 restores. The stepping magnet of CS--I operates self-interrupted and advances the wipers of CS-I until they reach the 11th step where the circuit to the stepping magnet CSMI and to relay I09 will be opened, allowing relay I09'to restore.

The line relays WI and I02 restore and the equipment is now prepared to handle another call when the distributor switch DSI again advances to the 1st step.

Referring now in greater detail to Fig. 2, the sub-station, line equipment, and the connector portion of the finder-connector link are exactly the same as described for Fig. 1. Corresponding elements in Figs. 1 and 2 are numbered with the same last two digits. The leads which are common to all of the lines and correspond to those connected to resistor I30 in Fig. 1 are connected to wipers 2I1 and 2 I8 of distributor switch DS--2 in Fig. 2. The bank contacts of wipers ZII and 2 I 8 of DS-2 are connected to the 11th bank contacts of wipers 2I2 and 2I3 of the corresponding finder switches. The finder switches in-Fig. 2 are returned to the 11th position after each call. All of the lines are thus normally extended through the back contacts of the associated line relays, wipers 2H and 2 I8 of the distributor switch, and wipers 2I2 and 2I3 of one of the finder switches to a vacuum tube 242 in one of the finders, in this case the first finder. The fllament circuit to vacuum tube 242 is closed from wiper 220 of DS-2. Vacuum tube 242 is normally biased to cut-ofi by means of the voltage drop in resistor 243. When a receiver is removed from the hookswitch at one of the substations the direct current flowing over the line through the back contacts of the associated line relay, wipers 2I'I and 2I8 of DS--2, wiper 2I2 and 2I3 of FS-2 and through resistors 244 and 245 reduces the net grid bias on vacuum tube 242. The plate current therefore increases and operates relay 205.

7 Relay 205 operates and closes the circuit to relay 203 and the stepping magnet FSM-Z of the finder switch F S-2 through its interrupter springs 249 from ground on the 11th bank contact of wiper 2I4 of FS-2.

Relay ,203 operates and prepares a multiple circuit to the stepping magnet FSM-2 from wiper 2I5 of FS-Z. The stepping magnet advances the wipers to the first set of bank contacts. The first line relay 20I operates from wiper 2I I.

If the first line is the calling line relay 205 will remain operated and will prevent further stepping of the finder switch as the circuit to FSM42 is opened by wiper 2l4. If the first line is already connected to another finder range there will be a ground on wiper 2 I 5 of FS-2 from the other finder that will cause this finder switch to step again even though relay 205 is operated. If the first line is idle there will be no potential across the line and the grid bias on vacuum tube 242 will increase to the cut-off value permitting relay 205 to restore. When relay 205 restores it recloses the stepping circuit to the finder switch from wiper 2I4 and causes the finder switch to continue stepping. The finder switch will continue stepping until the called line is reached at which time the net grid bias on vacuum tube 242 will be reduced by the direct current potential across the line causing relay 205 to operate.

Relay 205 operates and opens the circuit to relay 203 and the stepping magnet FSM2 of the finder switch FS2.

Relay 203 restores andcloses the circuit to relay 204 from wiper 2I4 of FS2, through make prings on relay 205. 5

Relay 204 operates, connects dial tone to the calling line to inform the subscriber that the equipment is prepared to receive impulses from the calling device, closes the filament circuit to vacuum tube 246, closes a multiple circuit to the filament of vacuum tube 242, grounds wiper 2I5 of the finder switch FS-2 to prevent other finders from stopping on the same line, grounds wiper 222 of the connector switch CS-2, closes the circuit to relay 296 from the 11th bank contact of Wiper 225 of CS--2, closes the circuit to the stepping magnet DSM2 of the distributor switch DS-2 through its interrupter springs 25!) and wiper MS of DS 2, and removes a multiple ground from the 11th bank contact of wiper 219 of DS-2.

The distributor switch advances to the next idle finder as previously described for Fig. l. The succeeding operations for connecting to the called line, testing to see that the line is free, signalling the called party, and establishing a transmission circuit are identical to those described for Fig. l. The only difference in the two figures after this point occurs when both parties restore their re ceivers to the hookswitch, allowing relay 2% to restore. Relay 285 releases relay 284 which restores and closes the self-interrupting circuit to the stepping magnet CSM2 of the connector switch CS2 from wiper 225 of CS2 thru its interrupter springs 258, causing it to return its wipers to the 11th step. Relay 284 also closes the self interrupted circuit to the stepping magnet FSM-Z of the finder switch FS-Z from Wiper 2M of FS-Z through its interrupter springs 249, causing the finder switch to restore its wipers to the 11th step.

Having described and illustrated my invention,

what I consider new and desire to have protected by Letters Patent will be pointed out in the appended claims.

What I claim as my invention is:

1. In an automatic telephone exchange system, telephone lines entering the exchange, local battery telephone substations on each one of said lines, each provided with a local battery arranged to energize the transmitter thereat, circuit arrangements for setting up a current flow from the local battery at a calling substation over the associated line to the automatic exchange solely by the removal of the receiver from the hookswitch, automatic switches in the exchange, and means responsive to said current flow to effect a connection between a calling line and an automatic switch in the exchange.

2. In an automatic telephone exchange system as claimed in claim 1, a calling device at each local battery substation arranged to interrupt the said current flow in accordance with th digits in the telephone numbers of called subscribers, a space discharge device in said automatic switch, and means controlled by said space discharge device for directing said automatic switch in response to said interruptions of said current flow to set up connections to said called subscribers.

3. In an automatic telephone exchange system, telephone lines entering the exchange, local battery telephone substations on each one of said lines, each provided with a local battery arranged to energize the transmitter thereat, circuit arrangements for setting up a current flow from the local battery at a calling substation over the associated line to the automatic exchange, a plurality of finders having access to said lines, means for operating one of said finders into association with said lines successively, a vacuum tube in said finder, means for associating the control element of said vacuum t e with said lines successively in order to test the lines as the movement of the finder progresses, and means controlled by said vacuum tube for terminating the operation of the finder in response to said current flow and for seizing the calling line when it is reached.

4. In an automatic telephone exchange system, telephone lines entering the exchange, local battery telephone substations on each one of said lines, each provided with a local battery arranged to energize the transmitter thereat, a common circuit, circuit arrangements for setting up a current flow from the local battery at a calling substation over the associated line to the automatic exchange, a plurality of finders having access to said lines, a vacuum tube common to said finders, means associating the control element of said vacuum tube with said common circuit, and means controlled by said vacuum tube in response to said current flow for operating one of said finders into association with said lines successively.

5. In an automatic telephone exchang system, telephone lines entering the exchange, local battery telephone substations on each one of .said lines, each provided with a local battery arranged to energize the transmitter thereat, a common circuit, circuit arrangements for setting up a current flow from the local battery at a calling substation over the associated line to the automatic exchange, a plurality of finders having access to said lines, a vacuum tube common to said finders, means associating the control element or said vacuum tube with said common circuit, means controlled by said vacuum tube in response to said current fiow for operating one of said finders into association with said lines successively, means for disassociating said lines successively from the control element of said vacuum tube, and means controlled by said vacuum tube for terminating the operation of said finder when the calling line is reached and disasseciated from said control element.

6. In an automatic telephone exchange system, telephone lines entering the exchange, local battery'telephone substations on each one of said lines, each provided with a local battery arranged to energize the transmitter thereat,/a common circuit, circuit arrangements for setting up a current flow from the local batteryat a calling substation over the associated line to the automatic exchange, a plurality of finders having access to said lines, a vacuum tube common to said finders, means associating the control element of said vacuum tube with said common circuit, means controlled by said vacuum tube in response to said current flow for operating one of said finders into association with said lines successively, a second vacuum tube individual to said finder, means for associating the control element of said second vacuum tube with said lines successively in order to test the lines as the movement of the finder progresses, and means controlled by said second vacuum tube in response to said current flow for terminating the operation of the finder and for seizing the calling line when it is reached.

7. In an automatic telephone exchange system, telephone lines entering the exchange, local battery telephone substation on each one of said lines, each provided with a local battery arranged to energize the transmitter thereat, a common circuit, circuit arrangements for setting up a current flow from the local battery at a calling substation over the associated line to the automatic exchange, a plurality of finders having access to said lines, a vacuum tube .in each finder, means associating the control element of one of said vacuum tubes with said common circuit, means controlled by said vacuum .tube for starting the operation of its associated finder in response to said current fiow, means for associating the control element of said vacuum tube with said lines successivelyas the movement of the finder progresses in order to test the lines, and means controlled by said vacuum tube for terminating the operation of the finder in response to said current flow and for seizing the calling line when it is reached.

8. In a automatic telephoneexchange system as claimed in claim 3, automatic switches in the exchange, a calling device at each local battery substation arranged to interrupt the said current flow in accordance with the digits in the telephone numbers of called subscribers, and means controlled by said vacuum tube for directing said automatic switches in response to interruptions of said current flow to set up connections to said called subscribers. n

9. In an automatic exchange system as stated in claim 6, automatic switches in the exchange, a calling device at each local battery substation arranged to interrupt the said current flow in accordance with the digits in the telephone numbers of called subscribers, and means. controlled by said second vacuum tube for directing said 11. In an automatic telephone exchange system, automatic telephone lines entering the exchange, local battery telephone substations on each one of said lines, each provided with a local battery arranged to energize the transmitter thereat, circuit arrangements for setting up a current fiow from the local battery at a calling substation over the associated line to the automatic exchange, a pluraltiy of finders having access to said lines, a vacuum tube common to said finders, and means controlled by said vacuum tube in response to said current flow for operating one of said finders into association with said lines successively.

12. In an automatic telephone exchangesystern, telephone lines entering the exchange, local battery telephone substations on each one of said lines, each provided with a local battery arranged to energize the transmitter thereat, a common circuit, circuit arrangements for setting up a current flow from thelocal battery at a calling substation over the associated line to the automatic exchange, a plurality of finders having access to said lines, a control device common to said finders, means associating said control device with said common circuit, and means controlled by said control device for operating one of said finders into association with said lines successively in response to said current flow.

13. In an automatic telephone exchange system, telephone lines entering the exchange, local battery telephone substations on each of said lines, each provided with a local battery arranged to energize the transmitter thereat, circuit arrangements for setting up a current flow from the local battery at a calling substation over the associated line to the automatic exchange, a

plurality of finders having access to said lines, means for operating one of said finders into association with said lines successively, a control device in said finder, means for associating said control device with said lines successively in order to test the lines as the movement of the finder progresses, and means controlled by said control device in response to said current flow for terminating the operation of the finder and for seizing the calling line when it is reached.

14. In an automatic telephone exchange system, telephone lines entering the exchange, 10- cal battery telephone substations on each one of said lines, each provided with a local battery arranged to energize the transmitter thereat, a common circuit, circuit arrangements for setting up a current fiow from the local battery at a calling substation over th associated line to the automatic exchange, a plurality of finders having access to said lines, a vacuum tube in each finder, means associating the control element of one of said vacuum tubes with said common circuit, and means controlled by said vacuum tube for starting the operation of its associated finder in response to said current flow.

15. In a selecting system, a plurality of lines, an automatic progressive movable switch, means controlled over any one of said lines for starting said switch and causing it to successively disassociate said lines from said control means and associate said lines with said switch, and means for terminating the operation of said switch when a particular line is reached and for maintaining that line in associaton with the switch.

16. In a telephone exchange system, telephone lines entering the exchange, a plurality of finders having access to said lines, means controlled over any one of said lines for starting one of said finders and causing it to successively disassociate said lines from said control means and associate said lines with said one finder, and means for terminating the operation of said one finder when a particular line is reached and for maintaining that line in association with said one finder.

1'7. In an automatic telephone system, an exchange, a plurality of telephone lines entering the exchange, a subscriber substation on each of said lines, each substation having a local battery arranged to energize the transmitter thereat, circuit arrangements for setting up a current flow from the local battery at a calling substation over the associated line to the exchange, automatic switches in the exchange accessible to any of said lines, a circuit common to said plurality of lines, and means responsive 'to said current flowing in said common circuit to effect a connection between a calling line and one of said automatic switches.

ROSWELL H. HERRICK. 

